Travelling through Dallas is a distinct possibility as it gives the best connections to get to Belize, a destination high up on my list.
Dallas/Fort Worth airport and Houston Intercontinental are both convenient to Belize. I have flown British Airways back and forth between DFW and London a couple times each way, and it was a nice flight. Long, but nice. US Customs in Dallas was pretty easy, too. DFW is easier to get around in than IAH (Houston). Houston is the forth largest city in the US, and the airport is rather old. Not a bad airport, but not easy to get around if you aren't familiar with it.
CD